Data transmission systems are well known and widely used to exchange information and conduct transactions with remotely positioned portable data devices. Such portable data devices are commonly referred to as cards, smart cards, or tags. Likewise, data transmission terminals are commonly referred to as card readers. In such a data transmission system, a transaction begins when a card enters the excitation field of the terminal/reader. In particular, the terminal produces a power signal as well as a data signal (also referred to as an information signal) and transmits the information signal using a carrier signal. It is the detection and reception of the carrier signal that remotely powers the card, and enables the card circuitry to perform its intended function.
Remotely powered (i.e., contactless) data devices (i.e., cards) can be used to perform a variety of tasks, including theft prevention, personnel or material identification and control, automatic fare collection, money and service transaction recording and control, and the like. While ID tags may be less complex, so-called smart cards tend to be more complex and may include one or more processors, as well as local memory to store and process information. A particular variety of the contactless IC cards (or contactless smart cards) is known as a vicinity card and uses a communication protocol called the ISO/IEC 14443 standard. Physical characteristics of a vicinity IC card, its radio frequency (RF) power and signal interface, and its initialization and anti-collision and transmission protocol are defined in ISO/IEC 14443. Specifically, two communication signal interfaces, referred to as type-A and type-B, are described in ISO/IEC 14443.
In the type-A interface, interfacing between a card reader (or a terminal) and an IC card is performed using the technique of amplitude phase-shift keying (ASK) 100% modulation of the RF operating field, and data to be transmitted are coded in the format of a modified miller code. In the type-B interface, interfacing between a card reader (or a terminal) and an IC card is performed using ASK 10% modulation and data to be transmitted are coded in a format of NRZ-L non-return-to-zero level (NRZ-L) code. Since the type-A and type-B interfaces are described in detail in ISO/IEC 14443, a detailed description about them will be omitted.
IC cards according to the Background Art support either the type-A or type-B interface. As described above, since the type-A and type-B coding and modulation are different from each other, an IC card supporting one of the communication signal interfaces can be used only in a card reader supporting the corresponding communication signal interface. If a card reader supports the type-A communication protocol, it is impossible to use with it an IC card supporting only the type-B interface, and vice-versa.